1. Field of the Invention
This invention relates to an actuator control method and storage device for detecting an actuator velocity from the counter electromotive voltage of the actuator, and particularly to an actuator control method and storage device for performing an unloading operation that moves the head which reads the storage medium away from the storage medium when not in use (when there is no access command within a specified time).
2. Description of the Related Art
Storage devices that have a head for reading storage medium are widely used. For example magnetic disk drives used as storage devices for computer comprise a magnetic disk, a head for reading from and writing to the magnetic disk, and a VCM actuator for positioning the head on a track of the magnetic disk. The storage density of these kinds of disk drives is rapidly increasing, and compact disk drives are currently being developed for them. Compact disk drives are separate and portable, and can also be used as the external storage device of a portable handheld computer.
Hard disk drives comprise a magnetic disk, a magnetic head, a VCM actuator, and a flexure (suspension). In this kind of hard disk drive, as the density of the magnetic disk has increased in recent years, the distance that the magnetic head floats above the magnetic disk has decreased. Therefore, the magnetic head can easily come in contact with the magnetic disk by even a small vibration and damage both the disk and head.
In order to prevent this, a hard disk drive has been proposed (for example in Japanese Unexamined published patent No. H6-60578) in which a ramp is installed at a position away from the magnetic disk, and when the head is not in operation, it moves to the position of the ramp so it is out of the way (this is called the unloading operation).
Recent hard disk drives and the electronic devices (computers, etc.) in which they are installed have become more and more portable. Therefore, the hard disk drive is used in an environment in which it is easy for it to receive external vibration. Moreover, since the electronic devices are driven by battery, the capacity of the power supply is limited. Therefore, it is desirable to reduce the power consumption.
To meet this demand, in conventional storage devices, a continuous time of no access (I/O command) is counted, and when it reaches a specified time, the aforementioned unloading operation is performed and the head is moved away from the magnetic disk. In this method, when no access continues for a specified time, the head moves away from the magnetic disk, so it is possible to prevent damage to the disk and head even when there is external vibration. Also, since the head is supported mechanically by the ramp, there is no need for drive current to flow to the VCM, so it is also possible to reduce the power consumption. Moreover, when there is access, the head returns from the ramp to the magnetic disk (this is called loading), and in this way the head is loaded only when in operation.
However, the prior art has the following problems.
(1) In the prior art, the moving velocity of the head is not controlled during loading/unloading. In the storage device, the servo information (position information) recorded on the disk is read by the head and the velocity and position of the head are detected. However, since the head is separated from the disk during loading/unloading, the servo information cannot be read, thereby the velocity cannot be detected. Therefore, there is the problem that during unloading, the head may hit the ramp, or that during loading, the head may hit the disk. There is also the problem that when decreasing the velocity of movement during loading/unloading in order to lighten this impact, it is impossible to perform high-speed loading/unloading.
(2) Also, detecting the velocity from the counter electromotive voltage of the motor (actuator) is well known, however a transient response occurs due to the motor inductance. Therefore, there it is necessary to wait until the transient response settled before detecting the counter electromotive voltage for detecting the velocity. Therefore, there is the problem that it is not possible to shorten the detection interval and thus making high-precision velocity control difficult.
(3) Moreover, in order to convert the counter electromotive voltage of the motor (actuator) into velocity, it is necessary to properly set the velocity offset coefficient. However, this velocity offset coefficient changes depending on each individual circuit and temperature, so there is the problem that it is difficult to properly set the velocity offset coefficient.
(4) Furthermore, in order to convert the counter electromotive voltage of the motor (actuator) into velocity, it is necessary to properly set a correction coefficient. However, this correction coefficient changes depending on the device and temperature, so there is the problem that it is difficult to properly set the correction coefficient.
The objective of this invention is to provide an actuator control method and storage device for controlling the actuator velocity even when the head cannot read from the storage medium during loading/unloading.
Another objective of this invention is to provide an actuator control method and storage device for shortening the interval of detecting the actuator counter electromotive voltage in order to perform high-precision velocity control.
A further objective of this invention is to provide an actuator control method and storage device for obtaining a proper velocity offset coefficient for converting the counter electromotive voltage of the motor (actuator) into velocity.
Yet a further objective of this invention is to provide an actuator control method and storage device for obtaining a proper correction offset coefficient for converting the counter electromotive voltage of the motor (actuator) into velocity.
In order to accomplish these objectives, the storage device of this invention comprises a head for at least reading the storage medium, an actuator for positioning the head at a specify location on the storage medium, a ramp for supporting the head and located at a position away from the storage medium, a storage means for storing specified parameters, and control means for unloading the head from the storage medium to a position on the ramp, and also for loading the head from the ramp at a position on the storage medium. In addition, the control means calculate the amount to control the actuator and calibrate the parameter when unloading or loading the head based on the output of a counter electromotive voltage detection circuit and the aforementioned parameters.
In this form of the invention, during unloading/loading when the head cannot read from the storage medium, the movement velocity of the actuator is detected from and controlled based on the counter electromotive voltage of the actuator and the parameters, so it is possible to control the velocity during unloading/loading, and thus it is possible to prevent the head from hitting the ramp and the storage medium, and high-speed movement is possible.
Moreover, since the parameters (transient response voltage, offset coefficient, correction coefficient, etc.) are corrected, accurate velocity control is possible.
In another form of the invention, the control means of the storage device, in order to detect the movement velocity of the actuator, updates the drive current of the actuator, then subtracts the transient response voltage of the actuator from the detected voltage of the actuator and calculates the counter electromotive voltage of the actuator and velocity of the actuator from the counter electromotive voltage. In addition, the control method for the actuator comprises a step of calculating the control amount for the actuator from the counter electromotive voltage of the actuator and the aforementioned parameters.
In this form of the invention, the transient response voltage of the motor is calculated from the drive current, and the counter electromotive voltage is calculated from the detected voltage of the motor and the transient response voltage by using the correction value (parameter) for the output of the counter electromotive voltage detection circuit, and by calculating the control amount with the calculated counter electromotive voltage, it makes high-precision velocity control possible.
In addition, in another form of the invention, the control means of the storage device flow drive current to the actuator with the actuator in a fixed state, and measure the velocity offset coefficient of the actuator. Moreover, the control method comprises a step of flowing drive current to the motor with the motor in a fixed state, and measuring the velocity offset coefficient of the motor, a step of detecting the counter electromotive voltage of the motor, a step of calculating the velocity of the motor from the counter electromotive voltage and velocity offset coefficient of the motor, and a step of controlling the velocity of the motor based on the detected velocity of the motor.
In this form of the invention, drive current flows to the motor while the motor is in a fixed state, and the velocity offset coefficient of the motor is calculated, so calibration of a proper velocity offset coefficient based on the device and temperature is possible.
Furthermore, in another form of the invention, the control means of the storage device measures the velocity offset coefficient during loading. No special measurement operation is necessary because automatic measurement is performed during the loading. Therefore, it is possible to reduce the waiting time of the storage device.
Moreover, in the control method of this invention, the measurement step comprises a step of flowing a first value of drive current to the motor in a fixed state and detecting a first counter electromotive voltage for the motor, a step of flowing a second value of drive current to the motor in a fixed state and detecting a second counter electromotive voltage for the motor, and a step of calculating the velocity offset coefficient of the motor from the difference of the two counter electromotive voltage.
This makes it possible to measure an accurate velocity offset coefficient.
In another form of the invention, the control means of the storage device corrects the correction coefficient for converting the counter electromotive voltage to movement velocity, based on the movement velocity of the actuator that is calculated from the position information that is read by the head from the storage medium, and the movement velocity that is detected from the counter electromotive voltage of the actuator.
In this form of the invention, the correction coefficient is corrected such that the movement velocity detected from the counter electromotive voltage matches the movement velocity of the actuator that is calculated from the position information from the storage device. Therefore, it is possible to convert the counter electromotive voltage into accurate movement velocity.
Furthermore, in another form of the invention, the control means of the storage device corrects the correction coefficient during unloading. This makes measurement possible without any special measurement operation. Therefore, it is possible to reduce the waiting time of the storage device.